It is well known that in many radiation detector applications the use of semiconductor devices affords substantial advantages. For example, in low energy radiation spectroscopy, semiconductor detectors have been used to achieve excellent energy resolution. On the other hand, in the field of high energy physics, position sensing of charged particles is still performed mostly with gas proportional or drift chambers. Because of the continuing desire to develop detectors with better energy resolution for use in the field of high energy physics, there has been for the last several years, a growing interest in the application of semiconductors as high resolution position sensing detectors for such particle physics applications.
One example of a semiconductor detector applied as a particle position indicating means is shown in U.S. Pat. No. 3,863,072, which issued Jan. 28, 1975. The disclosed wafer of doped semiconductor material is provided with a metallic thin film that is vapor deposited on one of its faces. As is also shown in the patent, it is well known in such detector applications to use semiconductor materials that are heavily doped with either n-type or p-type impurities. A common technique used in the manufacture of such prior art semiconductor particle position detectors is to mount electrodes on opposite major surfaces of a semiconductor wafer, with at least some of the electrotrodes subdivided into a plurality of parallel strips. One array of stripped electrodes is crossed with other stripped electrodes to form a so called checker board counter that allows the precise point where a particle enters the wafer to be positioned. U.S. Pat. No. 3,529,161, which issued Sept. 15, 1970, discloses such a known prior art type of semiconductor radiation particle positione detecting device. Also, U.S. Pat. No. 3,415,992 shows a semiconductor radiation detector having a readout arrangement with good sensitivity for obtaining highly accurate particle position readouts. The position resolution of particles by these disclosed devices is determined to a degree of accuracy that is dependent on the line density of the incorporated plurality of overlapping elongated contacts. Finally, U.S. Pat. No. 3,624,399, which issued Nov. 30, 1971, shows a radiation detector that is similar to those shown in some of the above mentioned patents, in that it comprises a semiconductor disk having crossing strip electrodes on its opposite sides to detect the position of particle developed charge carriers. The disclosed detector is characterized by incorporating means for reducing cross talk between the strip electrodes.
By way of further background for the invention disclosed herein, an example of a typical position sensitive silicon microstrip type semiconductor detector is schematically illustrated in FIG. 1. In this prior art type of detector, a single voltage provides the field for depleting the semiconductor crystal and the drift field for charge carriers that are produced in the detector by passage of ionizing particles through it. As illustrated, the detector consists of a thin n-type silicon wafer, which typically is approximately 300 microns in thickness. The wafer has a continuous n.sup.+ n junction on one of its sides and a strip pattern of p.sup.+ n junctions on its opposite side, as shown. To operate the detector, a suitable reverse bias voltage is applied across the wafer by a conventional source of electric potential (not shown), thereby to deplete the detector and to provide the desired collection field. When a fast charged particle passes through the detector, it produces electron/hole pairs that drift toward the electrodes under the influence of the applied electric field, as indicated by the arrows next to the plus and minus symbols shown for the electrons and holes in FIG. 1. Such motion of the charge carriers induces a signal in an external amplifier (not shown) which is suitably connected between the n.sup.+ p.sup.+ contacts. Position sensing of the charged particle in this type of detector configuration is determined by the p.sup.+ contacts. As explained more fully in several of the patents identified above, the principle of particle postion detection, in the type of detector illustrated in FIG. 1 usually requires the same number of amplifiers as the number of individual p.sup.+ contact strips used on the detector. In fact, it is possible to reduce the number of such amplifiers that is required, up to a factor of 10, by using charge division readout; however a price for such reduction is paid both in the resultant complexity of the readout channels and in the sacrifice of double track resolution. Furthermore, even when such charge division readout systems are utilized, the number of readout channels required per unit length of detector still remains undesirably large (normally in the order of 20 to 500 channels per centimeter of detector length). Other factors presently limiting the application of such microstrip silicon detectors are; the volume requirement, the heat dissipation problem and the connection problems inherent in the use of such a large number of readout channels. Accordingly, it remains desirable to provide a semiconductor charge transport device that can be applied in the high energy physics field to provide a high resolution particle position detector, which achieves such high resolution while requiring the use of hundreds of times fewer readout channels than are required by related prior art particle position detectors.